Monday, 24 November 2014

This time we
have a guest blog post from the TW:eed Team’s Rob Clack, about his recent
volunteer lab work uncovering fossil bones!

As I’m
retired and enjoy preparing fossils, it’s a pleasure for me to spend a day a
week helping out in Jenny’s lab in Cambridge.
Over the years, we’ve accumulated quite a lot of rock samples by doing
what we term ‘bulk collecting’. This
means looking at beds we know have yielded fossils in the past, and gathering
lumps that show nothing, in the hope that when we break them up in the lab,
we’ll find something interesting.

Some time ago, I
started looking at material like this that we’ve collected from quite high in
the Ballagan Formation sequence. This particular fossil-rich bed has already
yielded a large rhizodont cleithrum (see photo) and the partial lower jaw of a
large tetrapod called Crassigyrinus,
a secondarily aquatic animal with minute legs, as well as large lungfish bones. Almost everything we find is disarticulated,
which is to say that the animal died, its flesh rotted away and the bones came
apart before being buried and subsequently fossilised.

Large rhizodont
cleithrum (shoulder element), scale bar 1 cm

Most of the
time, I use a mounted needle to pick the matrix away by hand, watching what I’m
doing down a binocular microscope, with an air pump blowing across the specimen
to shift the tiny bits of rock I’m picking off.
For the harder rock, I use a dental mallet. This has an electric motor hanging from a
stand above me, with a flexible drive coming down beside me. On the end is a handpiece which translates
the rotary motion of the motor into a reciprocating movement to power a needle
in a tiny forward-and-backward motion.

Usually, after I’ve
exposed a small area of bone, I soak it in consolidant consisting of a clear
plastic dissolved in acetone. This
penetrates all the little cracks in the bone and glues them together, so they
don’t blow away as I expose more bone.
One advantage of this is that if I get it wrong and a piece of the bone
moves, I can dissolve the consolidant with more acetone, and move the fragment
into the right position.

Rob Clack at work preparing fossils in
the lab

The lumps of
rock we’ve got are not huge, so I’m unlikely to find anything as big in the lab
as we did in the field, but even so, there is quite a lot there, just waiting
to be found. A month or two ago, I found
a small tetrapod jugal bone. This is a
cheek bone that sits behind the eye, forming part of the margin of the orbit

More
recently, I’ve found skull bones of several small lungfish, a hyomandibular
bone (connected the jaw articulation to the braincase, strengthening the skull)
of a rhizodont fish, as well as several other rhizodont bones, part of the
skull table of a tiny tetrapod, and yesterday, an intriguing small bone, less
than a centimetre across, covered with tiny denticles. We don’t know what sort of animal it came
from, but it is unlikely to be a lungfish, since they didn’t have normal teeth,
just bony plates with radially-arranged conical ridges.

I’ve also
found plenty of fish scales of various sizes and types, spines, and quite a few
skull bones which are in internal view, making them very hard to identify. They’re too fragile to lift entirely off the
surface of the rock, so we may never know what animal they came from.

On the other
hand, one day we might find a more robust one that we can turn over, and then
we’ll be able to say “Oh, it’s one of those!” and slot another piece of the
jigsaw into place.

Thursday, 13 November 2014

Last week
member of the TW:eed Project presented their work at a prestigious
palaeontology conference. The Society of Vertebrate Palaeontology held their
annual meeting in Berlin this year. Among the thousand or so delegates were a
number of members of the TW:eed Project including Jenny Clack, Kelly Richards
and Tim Smithson from Cambridge.

Jenny and Tim on
arrival at Berlin Airport

Jenny gave a
talk on the evolution of the tetrapod limb skeleton based on specimens
discovered recently in the Scottish Borders and Nova Scotia. Delegates were
amazed by the number of new specimens that have been found and how varied they
are.

A poster on
the new sharks from the Scottish Borders was also presented. This included
photographs of some of the teeth that Becky Bennion had prepared during the
summer during her work placement.